Check your .profile in your user home direcotry may have an outdated entry.
If your file contains the line: export QT_SCALE_FACTOR=1.xx you can remove or just change the value to 1.0.
This originally solved some visual issues with QT apps, but has been since resolved by other methods. I would leave it set at 1.0, just in case a QT app you install has some rendering issues or you can just comment it out.
note: changes take effect only when logging out and logging back in.
